The demand for high density mounting associated with the compacting and thinning of electronic devices has been rapidly increasing, particularly for applications in portable electronic devices such as mobile phones. Accordingly, for semiconductor packages, the surface mounting type suitable for high density mounting has become mainstream in place of the conventional pin insertion type. In the surface mounting type, a semiconductor device with a semiconductor element resin-sealed thereto is directly soldered to a printed board, etc., for secondary mounting with a connecting terminal such as a solder ball interposed therebetween.
Here, for applications in portable electronic devices, impact resistance is required because impacts from falling are often applied. On the other hand, in secondary mounting as described above, a space between a primary mounted semiconductor device and a wiring substrate is filled with a sealing resin in order to secure connection reliability between the primary mounted semiconductor device and the substrate. As the sealing resin, liquid sealing resins are widely used, but it is difficult to adjust the injection position and the injection amount of the sealing resin because the sealing resin is liquid, or in the case of a relatively large solder ball for secondary mounting, the gap between the solder ball and the substrate becomes wide to increase the injection amount. Accordingly, a technique has been proposed in which using a thermosetting resin sheet, a region in the vicinity of the connection part between a solder ball and a secondary mounted substrate, rather than the whole space between a semiconductor device and a substrate, is intensively reinforced (Patent Document 1).